1. Field of the Invention
The present invention relates to a universal interface between a number of different probes and various pieces of test and measurement equipment and, in particular, to a universal interface for an active or passive probe connecting to an oscilloscope or spectrum analyzer.
2. Statement of the Problem
The interface between a probe and a piece of test and measurement equipment such as an oscilloscope or spectrum analyzer must utilize a minimum number of connections and yet must enable a large number of different circuit functions along with the conventional RF BNC signal connector. This is especially true when a large number of different active or passive probes interface with the same test and measurement equipment. Probes have different operational characteristics such as attenuations, offset gains, input impedance requirements, and features such as AC coupling and DC reject. Probes have different control and power requirements. The probe generally has a probe pod for connecting to the test and measurement equipment. The probe pod may contain power supplies and circuitry as well as a connector. A need exists to provide a universal probe interface for a large number of different active and passive probes and a piece of test and measurement equipment.
Conventional probe interfaces provide an attachment to the test and measurement equipment that is sometimes difficult for the user to connect. Some prior probes have multiple cables for connections--for example, separate cables for RF and for power. The separate cables sometimes connect at different interface locations on the equipment or to other pieces of equipment such as an external power or control box. A need exists to eliminate the use of separate cables and to provide an interface connection with a minimum number of connections, but with a maximum interface intensity including the conventional BNC connection at a single location on the test and measurement equipment.
Such conventional probe interfaces only provide fixed voltage supplies from the test and measurement equipment to the probe and/or provide voltage sources or regulators within the probe that add weight, occupy large volumes of space, and add heat to the probe pod. A need exists to eliminate the use of voltage sources and regulators in the probe pod so as to minimize the weight, the space, and the heat in the probe pod so as to provide a minimum size for probe pods having minimum circuitry and power.
Conventional probes connected to test and measurement equipment such as oscilloscopes or spectrum analyzers do not automatically and completely set up the test and measurement equipment with respect to input impedance, attenuation, offset range, scale (i.e., units of measure displayed), and other probe features (e.g., DC reject, AC coupling, etc.). For a probe using a resistor I.D., even when automatically identified, the operator must also perform other tasks to completely set-up the probe such as manually setting the input impedance (e.g., 50 ohms input impedance for a 10:1 active probe). The operator must be assured that the probe is properly identified and the test and measurement equipment correctly and completely configured. Such conventional probes and their interface connections are difficult to use especially if manual configuration is required. A need exists to be capable of identifying a large number of probes (including future probes) upon installation to provide automatic and complete set-up of features for the identification of probes without operator intervention.
Many probes require the delivery of offset current through the interface. A need exists to calibrate zero offset current at the interface connection so that probes can be used without calibration.
With many probes available for use by an operator, it is imperative to know when a probe has been disconnected and when a new one has been connected. Hence, a need exists to immediately sense when a probe has been disconnected from the test and measurement equipment and when a new probe has been reconnected.
Some conventional probes have a male BNC connector with a pogo pin for interfacing with a female BNC connector and a probe identity ring around the female BNC connector. A need exists to provide a universal interface connection to the ring so that the universal interface operates to identify such conventional probes.
Some conventional probes have specific power supply voltage requirements. A need exists to provide a range of power supply voltages in a universal interface with a minimum of interface connections.
3. Solution to the Problem
The present invention provides a solution to the above needs as set forth next in the Summary of the Invention.